<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>map</title>
</head>
<body>
<script>
    let arr = ['1','20','-5','3'];

    let newarr = arr.map(s=>s<0?Math.abs(s):s);

    console.log(arr);
    console.log(newarr)

</script>
</body>
</html>